Such a component made of layers of material layer and electrode layer that are stacked one on top of another and in a manner alternating with one another is generally known as a stack. The currently best-known electronic component of this type is a stack that is generally known as a piezo actuator, which is used as an actuating element in injection valves of a large variety of engine types for motor vehicles. The material layers are ceramic layers in this piezo actuator.
Usually, such a stack has a rectangular or square cross section when observed in plan view. Electrical contact is made with the stack on two opposite circumferential sides. In order to be able to carry this out in a technologically careful manner, in the past the electrode layers were geometrically laid out such that only every second electrode layer extends laterally as far as one of the two circumferential sides, while the other electrode layers in each case do not extend as far as this circumferential side. The same goes in an analogous manner for the other circumferential side of the stack.
Furthermore, what are known as fully active stacks are known, in which the electrode layers and the material layers have the same area, with the result that all of the electrode layers each extend as far as the opposite circumferential sides. Since all of the electrode layers of the component extend as far as the two opposite circumferential sides, contact has to be made in a different way.
DE 101 53 770 A1 discloses a method for making contact with a stacked piezoelectric device. In this method, every second electrode layer is provided with an electrically insulating layer in an alternating manner on both sides. Subsequently, the exposed electrode layers of each circumferential side are connected together via a conductive layer. The conductive layer used is a resin which contains conductive particles.
DE 10 2006 003 070 B3 discloses a method for making electrical contact with a component in the form of a stack, said component consisting of material layers and electrode layers. For making contact, an insulation layer is applied to two opposite sides. Subsequently, each insulation film is opened by laser patterning at the position of every second electrode layer. Subsequently, the electrode layers are connected together on every circumferential side by way of an electrically conductive material.
Generally, on account of given requirements, high temperature resistance of the actuator and high durability are demanded. Essential for this purpose is good connection of external electrodes to the very thin electrode layers of the stack. If the electrical connection of the external electrodes to the electrode layers does not have low impedance or is flawed, excessive current densities and thus increased temperatures can occur locally, and this can result in permanent loss of contact in the worst case. This problem occurs in particular when the material of the external electrodes which make electrical contact with the electrode layers on the opposite circumferential layers is formed from a conductive adhesive. A conductive adhesive comprises electrically conductive particles, for example made of silver, gold or any other desired metal or a metal alloy, which are embedded in an insulating backing material, for example a polyimide resin, an epoxy resin, etc.